The present invention generally relates to monitoring cloud point temperature, crystallization and energy content of diesel fuel in cold temperature conditions. More specifically, the present invention relates to a device for monitoring cloud point temperature of diesel fuel onboard vehicles in cold temperature conditions.
Diesel is the most common form of fuel for heavy-duty trucks of the shipping industry worldwide. Due to its high-energy content and thus better fuel economy, diesel is also widely used by passenger cars in many countries. Especially in Europe, where more than twenty percent (20%) of passenger vehicles are powered by diesel. Diesel engines become inoperable when the fuel temperature falls below the cloud point of the fuel, due to wax crystals forming in the fuel and plugging the fuel tank filter. The formation of wax crystals in the diesel fuel is commonly referred to as gelling. Blending, cold-flow additives, fuel heaters and engine idling are all ways to mitigate the formation of wax crystals in diesel fuel, but these methods are all associated with important drawbacks and costs.
Blending is typically done in petroleum refineries, when cold weather is anticipated. A lighter fuel such as kerosene/jet fuel (commonly called No. 1 diesel in the U.S.) is blended into the regular diesel (No. 2 diesel in the U.S.) to lower the cloud point of the latter. However, blending is costly to the refineries, because kerosene/jet fuel commands a significantly higher market price than diesel fuel. Not only does the blended diesel cost more to produce, it also has lower energy content and poorer lubricity that decreases fuel economy and increases maintenance for the diesel vehicles. Fuel and maintenance are the main operating cost factors for the shipping industry. Moreover, blended diesel fuel supplied by one refinery cannot always address the cloud point needs of a large geographical region, where ambient temperature can vary significantly from one location to another. Nor does it always address the needs of the shipping industry, where trucks travel long distances. Consequently, it is common practice for many truck fleets, bulk fuel suppliers and individual truckers to perform their own blending of No. 1 and No. 2 diesels to meet the needs of their routes. Unfortunately, due to the lack of cloud point information, blending is often performed with little guidance other than past experience or guessing. Rough blending ratios of No. 1 and No. 2 diesels such as 1:1 or 1:2 are used, frequently without the knowledge of the cloud points of the diesel fuels that are being blended. Furthermore, without a cloud point analyzer, the final cloud point of the blended mixture cannot be verified. Over-dosing with No. 1 diesel is costly; while under-dosing could still render the vehicle inoperable in cold days. It should also be noted that fuel blending is often messy, cumbersome, and prone to inadvertent spillage. Fleet managers often instruct truck drivers to carry small quantities of fuel, such as fifty (50) gallons at a time during a long-haul route in cold weather, as compared to the typical one-hundred and twenty-five (125) gallons that can normally be carried. Such frequent stoppage for fuel greatly increases travel time; however, it does provide seasonably adjusted fuel along the route and thus lessen concern with gelling of the fuel.
Cloud point and related cold-flow properties of diesel fuels is information that is not traditionally provided to the consumer. For their peace of mind, many drivers often purchase costly cold additives with the intention of improving the cold-flow properties of their diesel fuel. However, without the knowledge of the fuel""s cloud point, drivers actually do not know whether the diesel fuel requires any additive at all. There exists the possibility that the money spent on the additive is wasted, as the cloud point of the fuel may already be adequate for the journey. Even after the additive treatment, the drivers cannot check for any improvement offered by the additive, as there is no available means to validate improvement. It is usually very important with cold additives that the dispensing of the additive must precede any cold weather. This is because once the wax crystals begin to form, no amount of additive can reduce the wax crystals or salvage the loss of operability of the vehicle. The main problem with most cold additives available on the market is that they cannot significantly improve cloud point. They do not reduce the mass or amount of wax formation or the viscosity of the fuel. They can only claim the ability to reduce the dimensions of the individual wax crystals, if diesel fuel of compatible chemical composition is treated. In actuality, the number of wax crystals becomes larger because the total mass of crystallization cannot be changed by chemical additives. Whether or not this larger number of smaller wax crystals can pass through the fuel filter of the vehicle cannot be predicted, as there are multitudes of vehicle types and fuel-additive chemical systems. Finally, modification of the waxing properties of fuels using aftermarket fuel additives is generally not recommended by engine manufacturers and refineries, because of possible incompatibility with other additives already contained in the fuel.
Expensive fuel heaters can be added onto diesel vehicles to prevent gelling of the fuel. These fuel heaters are commonly located at the filter, fuel tank and delivery lines. The more common form of fuel heater creates heat using resistive elements powered by an electrical source of the vehicle. Alternatively, engine heat can be used through direct heat transfer to the fuel, or indirect transfer through a liquid medium such as engine coolant. The limitation is that all of the above heating methods are available only while the engine is running. These methods are therefore most useful when the vehicle is moving. They cannot help when the engine is stopped; for example, while the vehicle is parked overnight. In addition, warm fuel does not burn nearly as well as cold fuel and can result in poor fuel economy. Condensation often results in fuel tanks that go through this type of heat/cool temperature cycle. This can promote the growth of algae; therefore, drivers are often advised to run the heater only when needed. Some heavy-duty trucks are equipped with an automatic engine-starting-and-stopping feature based on the engine coolant temperature. This feature is not popular because many drivers do not want the engine running unattended. Moreover, engine coolant temperature is not indicative of fuel gelling and does not reliably serve as a control signal. Cloud point is a much more appropriate indicator for this operation.
Many heavy-duty diesel vehicles are left idling during cold winter nights to ensure that the fuel is kept above the cloud point by the heat generated from the engines and the heaters. The consumption of fuel/electricity is significant, not to mention the impact on the environment due to the idling. Impending EPA regulations are expected to severely curtail truck idling during cold weather. The idling is done because drivers have no knowledge of the cloud point of the fuel relative to the ambient temperature. If the cloud point is known in conjunction with the forecast temperature for the night, the drivers can make a more informed decision. This will significantly reduce the anxiety of the drivers, in addition to saving fuel and reducing pollution. The same concern with fuel gelling overnight also applies to passenger car owners, who may not have the means of parking their vehicles in heated or sheltered areas during cold nights.
Knowing the cloud point of the fuel in use, one can minimize and, in certain situations, completely avoid the drawbacks of the above-mentioned methods. In order to incorporate an analyzer into the fuel system of a diesel engine, there are important restrictions to be satisfied. These restrictions are often not considered or applicable for currently available cloud point instruments designed for use in laboratories or refinery process areas. For instance, as space is in short supply in a vehicle, the size and weight of the device becomes a key issue. Equally important is the manner in which the device is implemented, due to its proximity to a large amount of highly flammable material. There are additional requirements for on-board testing devices of diesel fuel in a vehicle. For example, the device must have a minimum demand on utilities such as gas, coolant and electricity, as they are either not conveniently available, or available only in limited quantity. Moreover, a land vehicle-mounted device must be rugged enough to withstand vibrations on the road and whereas a boat-mounted device must be able to withstand orientation change and vibrations in a rough sea. Most of the currently available instruments to test cloud point are large, use specialized gases and fluids, and are too delicate to mount on vehicles.
It is an object of the present invention to provide an onboard vehicle device for determining the cloud point of fuels used in a diesel engine to ensure that the engine is operated reliably and efficiently in cold temperatures.
It is another object of the present invention to provide an onboard vehicle device for determining cloud point to approximate wax buildup and energy content of fuels used in a diesel engine.
A cloud point monitoring device which includes thermal conductive surface, cooler, temperature sensor, detection volume, detection wall unit, fiber optic cables for transmitting light, lighter emitter, light detector, and a data acquisition and control unit. The cloud point monitoring device provides an instrument to accurately measure the cloud point of diesel fuel, indicate the approximate level of crystallization in diesel fuel that has been chilled beyond its cloud point and indicate the approximate energy content of diesel fuel. The cloud point monitoring device design allows it to be made small enough to be mounted in a fuel system of a vehicle.